The need for security in systems utilized in various types of financial, governmental, retail, manufacturing and other establishments, in order to prevent use of the system, or entry into the system, by unauthorized parties is a current and pressing problem. One means for solving this problem is to provide reliable means to verify that the party requesting use of, or entry into, the system is in fact the person he or she claims to be. For the purpose of verifying the identity of an individual, some personal characteristic may be employed.
One suitable characteristic is the force pattern of an individual's signature. Systems have been developed which are capable of distinguishing between a forged signature and a valid signature on this basis. This may be accomplished by detecting individually distinctive force characteristics of a signature to be tested and converting them into electrical signals which can be automatically processed and compared with the stored representation of an authentic signature, for determination of whether or not the tested signature is a valid one.
A number of U.S. Patents have issued which are directed to signature verification, including U.S. Pat. Nos. 3,618,019; 3,818,443 and 3,859,515.
One of the requirements for a signature verification system is an apparatus on which the person whose identity is being tested can write a signature or other data, which apparatus is capable of converting the forces applied in the course of writing the signature or other data to electrical signals. Such a "writing table" thus serves the purpose of generating an analog signal consisting of voltage amplitude variations as a function of time which accurately represents the variations in amplitude of the applied force, as a function of time, required to write a given signature or other data pattern.
The writing table, in order to serve its intended purpose, must satisfy certain minimum requirements. First, the writing surface must be sufficiently large and stable to be convenient and comfortable to the signer, and should not exhibit perceptible motion when being written upon. Also, the writing table must be stable, not easily damaged by external abuse, not influenced by external vibrations, and able to withstand excessive pressures or impact loads without damage. In addition, the writing table must be capable of generating an analog electrical signal with an amplitude directly proportional to the vertical force applied to the writing surface; that is, the relationship of force to voltage must be related by a constant and predetermined calibration factor, which must be independent of the location on the writing surface at which the force is applied. The usable frequency response of the table must be at least 0 hertz (steady state) to 125 hertz, and must be free of resonant or harmonic distortion.
Examples of prior art writing tables intended for use in connection with signature verification systems are shown in U.S. Pat. Nos. 3,563,097; 3,956,734; 3,991,402; and 4,008,457.